In usual dynamic channel assignment algorithms for cellular systems, the same channels are assigned in cells with a constant separation. Recently, a new channel assignment scheme was proposed, in which the same channel can be assigned with less separation than usual if the CIR (carrier-interference ratio) is more than the desired value.The channel assignment problem mentioned above is known to be intractable (NP complete) problem in graph theory. We propose applying Hopfield's neural networks to the channel assignment problems in cellular systems. It is said that Hopfield's neural networks can solve optimization problems very quickly. The computer simulations show that the neural networks are useful for the effective utilization of channels.